The invention relates to an apparatus for making plastic tubes according to the preamble of claim 1.
In an apparatus for making in particular transversely grooved plastic tubes two sequences of die halves each circulating in an endless track are provided. The tracks border each other along a working section in such a manner that opposite die halves of the two tracks each form a continuous hollow mold for such a tube. Into this continuous hollow mold the plastic tube is extruded and by establishing a pressure gradient between the interior of the tube and the outside thereof applied shapingly to the die walls. This tube moves jointly with the two die sequences until it has adequately cooled and solidified and the two die sequences move apart again on passing through their endless track.
To enable tubes to be made with such an apparatus which at selective different intervals have sections of different shaping, for example end sleeves, according to the known apparatus forming the preamble (EP-A1 0 048 113) the die halves are provided with a plurality of different molding or forming passages. Said die halves are displaceable transversely of the longitudinal direction of a chain carrying them. Control slides for the displacement position circulate in guide rails which are provided with switching points. It is thus possible with the known apparatus by actuating the complicated points arrangement in the running extrusion operation to change from one for m of the tube being made to another. It is thus possible with the known apparatus to make tubes having differently shaped sections continuously by extrusion.
Although the known apparatus is only intended for making tubes for example with end sleeves it is fundamentally also possible to make endless tubes of various types with this apparatus. For said endless tubes several forms are available so that when changing production from one tube form to another it is not necessary to interchange all the die halves, a changeover operation being sufficient.
However, the production changeover takes place relatively rarely so that the time gained with the known apparatus is not in proportion economically to the considerable investment costs and the wear liability of the very complicated apparatus forming the preamble. In addition, because of their high thermal and mechanical stressing the great number of switching members necessary are liable to cause trouble.